Embodiments of the present invention relate to fluid conductivity sensors, and more particularly, to a driving circuit for a fluid conductivity sensor.
High end sensors for detecting the electrical conductivity of a fluid, particularly an aqueous solution, in which the sensor is submerged have existed for some time. However, such devices suffer from numerous difficulties, particularly where the ultimate determination by the sensor is subsequently used in robotics or other embedded systems.
When measuring the conductivity of an aqueous solution, one difficulty encountered is the potential to contaminate the sensor's electrodes (called “fouling”). This occurs when a current is passed through the sensor's electrodes, which causes ions to collect at both the anode and cathode. Sufficient collection of these ions alters the measurements, due to ionic interference in the conductivity of the fluid under test.
Existing methods for measuring conductivity of an aqueous solution typically utilize a voltage swing across a single electrode. This voltage swing (typically from a fixed positive potential (+X volts) to the same negative voltage (−X volts)) reverses the attraction of the ions at the electrodes, thus preventing fouling. This method, however, requires a wide range of voltages. Typically, these voltages are arrived at through a voltage inverter, which increases the energy use of the circuit, increases the complexity of the circuit (e.g., the negative voltage must be regulated), increases the size of the circuit, and increases noise in the circuit.
Existing methods also do not make sufficient use of modern microcontrollers. Instead, a significant amount of the circuit is typically dedicated to the measurement and interpretation of the results. Examples of this would be compensating for op-amp parameters (such as input bias current, offset voltage, or the like). The result is increased power consumption with decreased sensitivity and accuracy.
Finally, existing methods typically provide data in ways which are difficult to integrate into robotics or other embedded systems. For example, the conductivity sensor output may be presented as 4-20 mA current loops (i.e., analog) or via a digital display. Both of these are difficult, if not impossible, to integrate into the vast array of modern systems which expect a digital output (such as other microcontrollers, computer monitoring systems, dataloggers, or the like).
It is therefore desirable to provide a driving circuit for a fluid conductivity sensor that enables a simpler method of obtaining measurement results, decreases power requirements, increases sensitivity and accuracy, and provides data in a digital form that can be transferred and utilized by further systems.